Self adjusting instrument

ABSTRACT

The invention is an instrument for cleaning and/or shaping and/or widening a channel that exists in or through a solid object. The design of the instrument the superelastic and shape memory properties of the material from which it is made, allow the inner volume enclosed by the instrument, its outer contour, or both to change as a result of the forces exerted upon it while working, thereby shaping the instrument to the three-dimensional contour of the channel. A preferred embodiment of the instrument is an endodontic file for use in the cleaning, shaping, and widening stages of a root canal procedure.

This application is the National Stage of International Application No.PCT/IL2005/000086 filed on Jan. 24, 2005, which claims priority toIsraeli application no. 160074 filed on Jan. 26, 2004, and whichapplication(s) are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is related to the field of tools. Specifically thepresent invention relates to an instrument for cleaning and/or shapingand/or widening a channel, existing in or through a solid object.

BACKGROUND OF THE INVENTION

Publications and other reference materials referred to herein, includingreferences cited therein, are incorporated herein by reference in theirentirety and are numerically referenced in the following text andrespectively grouped in the appended Bibliography which immediatelyprecedes the claims.

There are many situations in which it is required to use an instrumentfor cleaning out and/or shaping and/or widening a channel that exists inor passes through a solid object. One of the best examples illustrativeof the problem and of the shortcomings of the prior art is from thefield of dental instruments, specifically root canal procedures. Rootcanal procedure is one of the most demanding tasks for a dental surgeon.Root canal treatment consists of two stages: (a) shaping, cleaning, andwidening of the root canal and (b) obturation of the canal space. Thefirst stage is aimed at removing all tissue remnants, shaping the canalspace and disinfecting it, while the second stage is aimed at sealingthe root canal and preventing its recontamination. Failure to achieveeither of those goals may result in persistent apicalperiodontitis—associated with periapical bone resorption and occasionalor chronic suppuration.

In the simplest case, in which the canal is relatively straight and hasa relatively uniform circular cross-section, the work is carried out bystarting with a small diameter instrument (known as a dental file) andreplacing it with a series of increasingly larger diameter files untilthe desired final diameter of the canal is attained. If the canal is notstraight, using the conventional stainless steel files will mostprobably result in a poor quality of treatment. In cases in which thecurvature is not too great, nickel titanium alloy files are able toadapt themselves to the longitudinal curvature of the canal; thusachieving better results; however existing nickel-titanium alloy filescannot adapt themselves to changes in the shape or diameter of thecanal, therefore a series of files must be used to clean out a canal asis the case with stainless steel files. Also the use of any type ofexisting file in a canal having non uniform or non circularcross-section results in a canal that is either not completely cleanedout or one having a circular cross-section, the uniform diameter ofwhich is at least as large as the maximum width of the original canal.

The anatomy of a tooth is shown in FIG. 1. Topographically tooth 1 isdivided into two sections. The crown 2, covered by enamel 4, is thevisible part of the tooth. The root 3 is below the gums and anchors thetooth in place in the jaw bone. Within the dentin 6, which comprises theprincipal mass of the tooth, is located the pulp chamber 5 and one ormore root canals 7, both of which are filled with pulp 8.

FIGS. 2A to 2C illustrate the major steps of the root canal procedure.In the first step (shown in FIG. 2A) part of the crown is removed andthe pulp is cleaned out of the pulp chamber. In the second step (FIG.2B) the openings of the root canals are widened. Then (FIG. 2C) thecanal system is shaped, cleaned, and widened, removing all pulpparticles and infection. In a final step (not shown in the figures) theclean and disinfected root canals are obturated.

Endodontic failures are more common than the profession is willing toacknowledge. The commonly quoted success rates are based mainly onstudies carried out in teaching institutes and/or by endodontists.Nevertheless, surveys carried out on the general public indicate that inassociation with up to 58% of the endodontically treated teeth aperiapical lesion was evident (1).

This represents, most probably, a poor quality of treatment (1);nevertheless, it may also represent a basic flaw in the common approachto root canal treatment. Root canals are usually perceived as having agradually tapering diameter with a round cross section (FIG. 3A). Thismay be true for many upper anterior teeth; however, it is far fromreality in many of the bicuspids and molars. In these teeth ribbon-likeroot canals, with a flat cross section (FIG. 3B) are common (2). Theflat dimension of these canals is at the bucco-lingual plane, which isnot seen on a radiograph, and usually has its maximal width at 5 mm fromthe apex. This anatomy is especially pronounced in the second upperbicuspids, in distal roots of lower molars, as well as in many caninesand lower incisors. Additionally, canals with a tear-shaped crosssection (FIG. 3C) are common in roots that have two canals, such as themesial roots of lower molars and those of upper first bicuspids as wellas in many of the mesio-buccal roots of upper molars. The fact that allof these anatomical variations are not seen on a regular periapicalradiograph is one of the reasons for the common misconception andpresents a major obstacle in achieving the goal of high qualityendodontic treatment.

The traditional, common, approach for cleaning, widening, and shapingroot canals utilizes hand files having round cross-sections and astandardized cylindro-conic shape. Sequential use of files of increasingdiameter, with intermitted flushing with antiseptic solution, results ina canal in which a cylindro-conic gutta-pecha cone may intimately befitted in the apical part of the canal and used as a “master cone”. Withthe proper paste type sealer and accessory cones they are expected toseal the apical part of the canal. The common cleaning, widening, andshaping procedures are designed to adapt the apical part of the rootcanals to the form of these standardized master cones.

This common concept is based on the image of a root canal that has around cross section, which may gradually be enlarged by round files tothe shape of a standardized master cone. Although suitable for anteriorteeth, when applied in many posterior root canals, this approach mayoften lead to failure. Cleaning, widening, and shaping a flat root canalwith round files will frequently leave a remaining buccal and/or lingualrecesses along the root canal filling, untouched and full of tissueremnants, bacteria, or both (3,4). This will inevitably result infailure. Recent studies indicate that this problem is much more commonthan previously appreciated (2, 3).

When using traditional hand-held stainless steel files some of theserecesses are inevitably only partially cleaned. In FIG. 4 is shown a setof stainless steel K-files. A great deal of experience is necessary tochoose the proper length and diameter as the canal is cleaned out fromthe top to the bottom. When the root canal curves it is only possible tofollow the curvature by increasing the diameter of the canal. Thisproblem is illustrated in FIG. 5A. If the curvature of the canal becomesto great, generally near the apex of the canal, then one of twoundesirable situations arises. The first, shown in FIG. 5B, is that theprocess is terminated resulting in creation of a ledge in the canal anddebris in the untreated lower part of the canal. The second alternative,shown in FIG. 5C, is that the procedure continues until perforation ofthe tooth occurs, also resulting in a false canal or apex enlargement.One other major difficulty encountered during root canal treatment isshown in FIG. 5D; if one of the solid files breaks and can not beremoved, a not infrequent occurrence, then the root canal treatmentfails and the tooth is usually removed.

The hand-held stainless steel instruments are currently gradually beingreplaced by nickel titanium rotary files. As in the case of K-files,current leading nickel titanium rotary files are used as series ofinstruments with gradually enlarging diameters but, unlike the stainlesssteel files, are able to adapt longitudinally to the canal shape. Nickeltitanium rotary files are more efficient and allow the operator tocomplete a case in a somewhat shorter time. Unfortunately, thisefficiency has a price: the prepared canal is of a perfect round crosssection and the cleaning of the recesses in flat and tear-shaped canalsis not done.

Recognition of the above problem has led some professional authoritiesto consider a further enlargement of the apical part of the canals, to adiameter that will include the flat remaining parts. The preparation ofa root canal by enlargement for root canals having round, flat, andtear-shaped cross-sections is shown schematically in FIGS. 6A, 6B, and6C respectively. Such enlargement could not be safely done in bent rootcanals with traditional stainless steel instruments because of theirrigidity (3). Rotary nickel titanium files made it possible to enlargebent canals in a mesial root of a lower molar to accept a No. 45-50gutta-percha master cone. Nevertheless, this approach has two shortcomings: it may frequently lead to either unwanted excessive localthinning of the remaining root canal wall (2) or to the use of asingle-cone root canal filling in the apical third of the canal. Thefirst may lead to a higher frequency of vertical root fractures, whilethe second was discarded long ago for its inferior sealing abilities.Furthermore, in many cases the diameter required to really include therecesses is so large that it will cause a perforation of the canal wall(2) (see FIG. 6B and FIG. 6C).

The issue of cleaning, widening, shaping, and obturation of root canalswith non-round cross sections does not currently have an adequate,efficient solution.

It is therefore a purpose of the current invention to provide aninstrument that is capable of changing its interior volume, contour, orboth during use in cleaning and/or shaping and/or widening a channel,existing in or through a solid object, in order to shape itself to thechannel's three-dimensional contour.

It is another purpose of the current invention to provide an endodonticfile that is capable of cleaning and shaping and widening root canalshaving circular and/or non-circular cross sections.

It is another purpose of the current invention to provide an endodonticfile whose contour varies during use thus allowing the use of a singlefile for an entire root canal procedure.

It is yet another purpose of the current invention to provide anendodontic instrument that is sufficiently flexible to allow it to adaptitself longitudinally to the curvature of the root canal up to itsapical end.

It is still another purpose of the current invention to provide anendodontic instrument through which antiseptic solution can continuouslyflow into the root canal while working.

It is a further purpose of the current invention to provide anendodontic file that has significantly greater endurance and strengththan existing instruments used to perform root canal treatments.

It is another further purpose of the current invention to provide anendodontic file that requires significantly less time to perform rootcanal treatments than existing instruments.

It is a still further purpose of the current invention to provide anendodontic instrument that is significantly easier to use and has asignificantly shorter learning curve than existing instruments used toperform root canal treatments.

Further purposes and advantages of this invention will appear as thedescription proceeds.

SUMMARY OF THE INVENTION

The present invention can be realized in many different embodiments andhas applications in many fields in which it is necessary to clean outand/or shape and/or widen a channel, existing in or through a solidobject Examples of such applications can be found, for example, in suchwidely differing fields as drilling for oil, dental surgery, andmaterial machining. In order to best illustrate the many advantages ofthe instrument of the invention over existing tools, a specificembodiment of the invention for use in dental root canal treatment, oneof the most demanding applications for instruments of this type, hasbeen chosen as an illustrative and non-limiting example to be describedherein.

The preferred embodiment of the endodontic instrument of the invention,known herein as the SAF (self adjusting file) is a nickel titaniuminstrument of a unique self adjusting design. The SAF has an originalround cross-section to which it always tries to return as a result ofsuperelastic properties that are given to it. Simultaneously thisproperty combined with its unique geometry gives it an extreme abilityto adapt itself to the shape of the canal walls. When inserted into anarrow canal it will have a contour narrower than its original one,which will gradually increase with use, thus allowing it to be used as asingle instrument for the whole root canal procedure. Moving theinstrument of the invention in the root canal, preferably by rotatingthe instrument but optionally by moving it back and forth in a directionessentially parallel to the longitudinal axis of the canal or by causingit to vibrate, will result in the removal of a layer from all innersurfaces of the canal, to which it adapts itself, while graduallyattempting to return to its original round shape. The instrument willthus perform an ideal shaping, widening, and cleaning, without unwantedlocalized thinning of the root wall.

The unique design of the instrument allows it to adapt itself bothlongitudinally and in the cross section and thus follow the originalthree dimensional shape of the root canal. Thus, a canal with a roundcross section will be enlarged as round, while a flat canal will beenlarged as a flat canal of greater dimensions. Even the trickiestcanals, those with a tear shaped cross section, will essentiallymaintain their original shape. Further the design of the instrumentallows it to achieve different shapes and dimensions along the length ofthe canal, thereby allowing effective cleaning of the entire canalwithout excessive widening of the canal walls. The method of the priorart to extensively enlarge root canals in order to include in theirdiameter the flat or tear-shaped recesses is thus eliminated.

Due to the special open and/or hollow design, antiseptic solution cancontinuously flow into the root canal while working, thus savingvaluable time and improving the debridement and disinfection procedures.The constant flow also increases the efficiency of filing and preventsclogging the canal with dentin-mud and debris.

The structural design of the self adjusting file of the invention allowstop elasticity. In the extreme case of an instrument failure andbreakage inside the canal, specially designed extractors can be used toeasily remove the separated part of the SAF, no matter what the positionor depth of the broken-off part is in the root canal.

In a first aspect the present invention provides an instrument forcleaning and/or shaping and/or widening a channel that exists in orthrough a solid object. The instrument of the invention is characterizedin that its inner volume, contour, or both changes during use in orderto shape it to the three-dimensional contour of said channel. Inparticular the shape of the perimeter of the instrument adjusts duringuse to conform to the perimeter of the local cross section of thechannel at each radial plane located along the length of the instrumentthat is inserted into the channel.

The instrument of the present invention can be made from a superelasticmaterial and a material which either has or has been treated to give itshape memory properties. In a preferred embodiment, the instrument ofthe invention is made from a nickel titanium alloy.

Preferably a single instrument is inserted into the channel and used forthe entire procedure of cleaning and/or shaping and/or widening thechannel before being withdrawn. In some applications, more than one fileis used to clean, and/or shape, and/or widen the channel. If theinstrument breaks inside the channel, the broken piece can be withdrawnfrom without damage to the object containing the channel.

In a preferred embodiment of the instrument of invention, its body iscomprised of one or more longitudinal elements and one or morecircumferential elements. The longitudinal and circumferential elementscan have a three-dimensional shape chosen from the group comprising:blade shaped, polygonal prism shaped, rod shaped, curved shaped, andround shaped elements. The cross-sectional shape of the longitudinal andcircumferential elements can be chosen from the group comprising:polygonal, round, and curved shapes. The longitudinal elements and thecircumferential elements can be straight or curved. In a preferredembodiment, the number of longitudinal elements is at least one and thecircumferential elements are distributed along the longitudinal axis ofsaid instrument. In another embodiment, the number of longitudinalelements is at least one and the circumferential elements aredistributed along the longitudinal axis of the instrument. Thecircumferential elements in a given radial plane define the localcross-sectional shape of the instrument.

In a preferred embodiment of the instrument of the invention, thelongitudinal and circumferential elements define the instrument'sthree-dimensional shape. That shape being that of a body with an emptyspace surrounding the longitudinal axis and bounded radially by a wallhaving an open lattice-like structure.

In preferred embodiments of the instrument of the invention, at least apart of the outer surface of the instrument is constructed or modifiedin such a way as to allow the instrument to remove material from thewall of the channel when relative motion takes place between it and thewall. The relative motion can be rotational, translational, vibrational,or a combination of two or more of these types of motion. In oneembodiment, at least part of the outer surface of the instrument iscoated with a coating of an abrasive material, which can be for example,diamond powder, titanium nitride, or tungsten carbide. In otherembodiments, at least part of the outer surface of the instrument of theinvention is roughened, comprises numerous small teeth, or comprises acutting edge.

Preferably, fluid can flow into the channel and/or debris resulting fromthe cleaning and/or shaping and/or widening can be removed from thechannel while the instrument of the invention is inserted and working inthe channel. The fluid can flow and/or the debris can be removed via theinterior of the instrument and/or, in other embodiments via the spacebetween the wall of the channel and the outer surface of the instrument.

In preferred embodiments of the instrument of the invention, a uniformamount of material is removed from the wall of the channel, along theentire insertion length of the instrument in the channel, during theprocedure of cleaning and/or shaping and/or widening the channel. Inother embodiments, the instrument can be constructed such that differentamounts of material are removed from the channel wall at differentlocations along the insertion length of the instrument. The instrumentof the invention can be inserted into the channel such that it passesthrough the entire length or only a portion of the entire length of thechannel.

In preferred embodiments of the instrument of the invention, thecross-sectional shape of the channel, along the entire insertion lengthof the instrument, is essentially the same after the procedure ofcleaning and/or shaping and/or widening the channel as it was before theprocedure.

Another embodiment of the instrument of the invention comprises a longnarrow balloon, which is inserted into the channel and then inflated.

Preferred embodiments of the instrument of the invention are endodonticfiles. In this case, the channel is a root canal, and cleaning and/orshaping and/or widening of the channel comprises the cleaning, shaping,and widening stage of a root canal procedure.

In another aspect, the present invention supplies a method of using theinstrument of the invention for cleaning and/or shaping and/or wideninga channel that exists in or through a solid object. The method comprisesthe following steps:

-   -   inserting the instrument into the channel;    -   causing relative motion between the instrument and the wall of        the channel;    -   optionally, removing the debris resulting from the cleaning        and/or shaping and/or widening from the channel while the        relative motion takes place;    -   optionally, causing fluid to flow into the channel while the        relative motion takes place; and    -   removing the instrument from the channel when the cleaning        and/or shaping and/or widening have been completed.

In the case in which the instrument of the invention is an endodonticfile, the method of cleaning, and/or shaping, and/or widening a rootcanal comprises the following steps:

-   -   inserting the file into the root canal;    -   causing the file to move relative to the wall of the root canal;    -   optionally, removing the debris resulting from the cleaning,        shaping, and widening from the root canal while the file moves        relative to the wall of the root canal;    -   optionally, causing fluid to flow into the root canal while the        file moves relative to the walls of the root canal; and    -   removing the file from the root canal when the cleaning,        shaping, and widening have been completed.

All the above and other characteristics and advantages of the inventionwill be further understood through the following illustrative andnon-limitative description of preferred embodiments thereof, withreference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the anatomy of a tooth;

FIGS. 2A to 2C illustrate the major steps of the root canal procedure;

FIGS. 3A to 3C show root canals having different cross sectional shapes;

FIG. 4 shows a set of stainless steel K-files;

FIGS. 5A to 5D show some of the problems encountered in using prior artfiles to perform root canal treatments;

FIGS. 6A to 6C show the stages, according to the prior art, in preparingroot canals having different cross sectional shapes;

FIGS. 7A, 7B, and 7C are respectively perspective, front, andflattened-out, views of the instrument of the invention;

FIGS. 8A and 8B show cross-sectional views of the instrument of theinvention before being inserted into the root canal and inside a tearshaped canal respectively;

FIGS. 9A, 9B, and 9C show schematically the preparation of a root canal,using the self adjusting instrument of the invention, for root canalshaving round, flat, and tear-shaped cross-sections respectively;

FIG. 10 shows how the instrument of the invention adapts its shape as itis inserted up to the apical end of the root canal; and

FIGS. 11A to 11F show cross-sections of examples of differentembodiments of the instrument of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In general, the channels to be widened and/or cleaned and/or shaped bythe instrument of the invention are relatively long and narrow. Thesechannels will be described hereinbelow in terms of a single“longitudinal axis”, which is the line defined by the loci of the centerpoints of the channel along its length, and a multitude of “radialaxes”, wherein each such radial axis is defined by a line originating ata point on the longitudinal axis and perpendicular to the longitudinalaxis at that point. Rotation of a given radial axis around its origindefines the localized “radial plane”. The direction essentially parallelto the longitudinal direction will be known as the “longitudinaldirection” and the direction essentially parallel to one of the radialaxes will be known as the “radial direction”. Because the instrument ofthe invention conforms to the shape of the canal similar terminologywill be used to describe the principal axes of the instrument.

The instrument of the invention can be inserted completely to the end ofthe channel or only partially into the channel, in which case only partof the channel will be widened and/or shaped and/or cleaned. The lengthof the instrument that is inserted into the channel is known as the“insertion length” which term also indicates the depth of the channelthat is worked on by the instrument.

As an illustrative, but non-limitative, example of the instrument of theinvention embodiments of an endodontic file for performing root canaltreatments will be described hereinbelow.

The preferred embodiment of the endodontic instrument of the invention,known herein as the SAF (self adjusting file) is a rotary nickeltitanium instrument of a unique design. While current leading rotaryfiles must be used as series of instruments with gradually enlargingdiameters, the SAF is used as a single instrument for the wholeprocedure. When inserted into a narrow canal, whose nominal diameter isless than its own nominal diameter, the instrument is compressed, itssuperelastic property allowing it to adapt itself to the cross-sectionalshape of the walls of the canal in each radial plane along thelongitudinal axis of the canal. Rotating in the canal it removes tissueand debris from the canal and the canal wall. As the debris is removedfrom the canal wall, the super elastic property of the SAF causes it togradually expand with time in the radial direction while continuallymaintaining contact with the canal wall at every point. Thus material isuniformly removed from the dentinal walls of the canal until the desirednominal diameter is achieved.

A preferred embodiment of the SAF is shown respectively in perspective,front, and flattened out, views in FIGS. 7A, 7B, and 7C. The SAF 10 ismade of a nickel titanium alloy (Nitinol) and originally is given acylindrical shape. The walls of the upper end, the neck 12, are solidand are gripped by either the dental hand piece or are attached to ahandle for manual use. The main part of the body of the SAF is an open,lattice-like structure made up of longitudinal elements 14, that run thelength of the instrument from neck to tip 16 and short circumferentialelements 18 that connect adjacent longitudinal elements. In thepreferred embodiment shown in the figures, there are four longitudinalelements and the circumferential elements, in their undeformed state arearcs of a circle. In a radial plane containing circumferential elements,the circumferential elements that lie in that plane define thecross-sectional shape of the instrument in that plane. Both thecircumferential and longitudinal elements have a flat rectangularblade-like cross section. After manufacture, the Nitinol cylinder isconstrained in a mold and heat treated to give it its shape memoryproperty while changing its shape to cylindrical-conic.

The surfaces of the instrument of the invention that are in contact withthe walls of the canal are treated in some way to enable them to removematerial from the wall as the instrument rotates. One possible treatmentis to coat the surfaces with an abrasive material such as, for example,diamond powder, titanium nitride, and tungsten carbide, that will removedentin from the canal wall by friction as the SAF is rotated, thuscleaning out and enlarging the inside of the root canal. In otherembodiments, the surfaces in contact with the wall of the canal can bemanufactured with roughened surfaces comprising, for example numeroussmall teeth as in a file or a rasp. Alternately, these surfaces cancomprise a cutting edge similar to the edge on a drill bit. In someembodiments of the instrument of the invention, the surfaces in contactwith the canal wall can be relatively smooth and abrasive slurry can beintroduced into the canal to be trapped between the instrument and thewall.

The material scraped from the wall of the canal passes through theopenings in the lattice structure of the body of the SAF into the hollowinterior from which it can easily be removed by rinsing or suctionwithout stopping rotation of the instrument or withdrawing it from theroot canal. In other embodiments, the debris can also be removed via thespace between the canal wall and the instrument. The design allows forfluids, such as antiseptic or saline solution, to continuously flow intothe root canal, either through the center of the instrument or betweenthe outer surface of the instrument and the canal wall, while theinstrument is working, thus saving valuable time and improving thedebridement and disinfection procedures. The constant flow alsoincreases the efficiency of filing and prevents clogging the canal withdentin-mud and debris. Another advantage of the hollow structure of theSAF is that, in the extreme case of instrument failure and breakageinside the canal, the separated part of the instrument of the inventioncan be easily and safely removed, using specially designed extractors,no matter what the position of the broken piece of the instrument in theroot canal.

After part of the crown is removed and the pulp is cleaned out of thepulp chamber, and a sufficient access to the canal is obtained the SAFis inserted into the root canal. As the instrument is pushed into thecanal, its superelasticity allows it to be guided to the apical end ofthe root canal by following the path of least resistance (through thepulp rather than the much harder dentine). Prior art nickel titaniumfiles can also adapt themselves to the canal shape longitudinally butare unable to change their volume and contour as can the SAF.Additionally the solid structure of the prior art files makes them lessflexible than the hollow lattice-like structure SAF. In FIG. 10 is shownthe SAF adapting its shape as it is inserted up to the apical end of theroot canal.

The instrument is now moved relative to the walls of the root canal inorder to carry out the cleaning, widening, and shaping process. Themotion can be longitudinal, i.e. the instrument can be moved up and downin the canal; rotational; vibrational, i.e. the instrument can be causedto vibrate by connecting it to, for example, an ultrasound transducer;or a combination of these motions. In the preferred embodiment of theinvention the SAF is rotated either manually or by means of a dentalhandpiece. As the instrument rotates, the SAF's super elastic propertykeeps its elements pressed against the root canal wall in all the radialplanes along the length of the instrument.

FIGS. 8A and 8B show cross-sectional views of the instrument of theinvention outside of and inside a tear shaped root canal respectively.The views in the cross-sections shown in FIGS. 8A and 8B are in radialplanes wherein each such radial plane is located at and contains asingle set of circumferential elements. Since the axis of the SAFessentially lies on the longitudinal axis of the canal, each planeintersects the walls of the canal at right angles. The perimeter of theSAF in each of these planes is made up of eight segments—14 a to 14 d,the longitudinal elements, and 18 a to 18 d, the circumferentialelements. The material and structure of the SAF have three propertiesthat allow it to carry out the desired function. Firstly, thesuperelasticity of the alloy makes the device constructed from itextremely flexible, allowing it to be deformed to conform to the shapeof the canal at the position at which it is located. Secondly, thediameter of the original cylindro-conic state of the instrument isgreater than the diameter of the canal. Therefore the stress created inthe alloy by the deformation from contact with the walls of the canal asthe instrument is rotated and the super elastic property causing theinstrument to try to return to its original cylindro-conic shape. Theinternal force exerted in attempting this return to the original shapeconstantly pushes the elements of the device against the inner wall ofthe canal. Thirdly each element made of the super elastic alloy has theproperty of being able to stressed/strained up to 8% to 10% from it'soriginal shape, depending on the exact composition of the alloy, thusallowing the internal volume of the SAF to increase with time and itselements to remain in constant contact with the walls, even as materialis continually being removed from them. As the instrument rotates eachof the circumferential elements 18 a to 18 d changes in length and shapeindependently from the others, thus the instrument is able to conform tothe local shape of the canal wall.

The fact that the circumference of the instrument is divided into fourelements, each of which can independently change shape imparts to theSAF a degree of flexibility, an ability to adapt to the shape of theroot canal, and the ability to expand in size that goes far beyond thatof existing files. These properties can be further increased by buildingthe instrument with a greater number of peripheral elements, howeverincreased flexibility, etc. will be gained at the expense of thestrength of the device.

Thus, in the plane shown, as the instrument rotates, its cross-sectionalshape is constantly changing to conform to the shape of the canal walland the length of the circumference of the device in that plane isconstantly increasing as material is removed from the wall. This is tobe compared to the situation with existing files in which the shape ofthe canal is changed to conform to the shape of the file and the filesmust constantly be replaced with files of larger diameter in order toclean, widen, and shape the canal.

The description given hereinabove applies for each successive set ofcircumferential elements located in different radial planes along thelength of the instrument. The adaptation to the local shape of the canaland changes in contour and length of the circumferential elements thatcomprise each successive set is essentially independent of itsneighbors. This behavior explains how the instrument of the inventioncan deal with the common situation described hereinabove in which thecanal narrows along much of its length and then becomes wide near theapical tip before narrowing again. Because the instrument is moved(rotated) as a single unit, the amount of material removed from thecanal wall, which mainly depends on how long the instrument is revolved,is essentially constant along the entire length of the portion of theinstrument that is inserted into the canal.

For almost all cases, the deviations of the diameter of the root canalfrom its average diameter are such that the instrument of the inventioncan be designed to allow use of a single instrument to clean out thewhole length of the canal. In the preferred embodiments of theinvention, the outer surface of the instrument is uniformly treated toenable removal of material from the wall, in which case essentially thesame amount of material will be removed from the wall of the canal ateach radial plane along its entire length. However, the skilled personwill know how the instrument can be designed and treated to allownon-uniform removal of material at different positions along the lengthof the canal, if this result is desired for specific applications. Basedon statistical information regarding the dimensions of root canals froma large number of teeth, a single nominal width can be determined forthe instrument of the invention. It may be however, that it ispreferable to provide instruments having several different nominaldiameters, for example a small diameter for a narrow canal and a largerdiameter for wide canals. In any case, once the correct size instrumenthas been selected, the entire cleaning, widening, and shaping procedureis then carried out using only that instrument which, once inserted intothe canal, is only withdrawn at the end of the procedure. It is to benoted that in some cases, the channel to be worked on by the instrumentof the invention may have an exceptionally widely varying cross section,in which case more than one instrument, having different nominaldiameters, will have to be used to shape, widen, and clean the entirechannel.

The preparation of a root canal, using the self adjusting instrument ofthe invention is shown schematically FIGS. 9A, 9B, and 9C for rootcanals having round, flat, and tear-shaped cross-sections respectively.The figures are a series of images showing the stages of the cleaning,shaping, and widening step in the procedure. The images range from theuntreated root canal on the left to the canal at the end of theprocedure on the right. From the figures, it can be seen that therotating SAF removes a relatively uniform layer from all inner surfacesof the canal wall and therefore the final shape of the cleaned out canal(right image) is very close to that of the original canal. The shapingand widening are done by removing a minimal amount of the canal wall andtherefore without causing localized thinning of the root wall as is thecase in the prior art (see FIGS. 6B and 6C). Using the SAF to clean outthe root canal, the nominal diameter and shape of the canal at eachradial plane along its length is preserved. In other words the shapedand cleaned canal does not have an essentially circular cross sectionhaving a uniform cross-sectional area along its length as is the casewith the prior art.

Shaping, widening, and cleaning the root canal with one instrument,while flushing with a constant flow of antiseptic solution, maysignificantly cut down treatment time. Additionally shaping and cleaningthe root canal with one instrument eliminates the necessity of theoperator following complex and tricky flow charts in order to accomplisha simple root canal treatment procedure, as is demanded by currentleading rotary file systems.

Heat-softened gutta-percha methods can be easily adapted for obturationof the prepared root canal obtained with the instrument of theinvention.

Many variations in the choice of materials and especially in the designof the structure of the device are possible. For example, the devicedoes not have to be built from Nitinol but other types of material, suchas, for example, stainless steel, steel, plastic, nickel based alloys,and titanium based alloys can be chosen. Instead of havingcircumferential and longitudinal elements with a flat rectangularblade-like shape as described hereinabove the elements can have, forexample, polygonal prism, rod-like, or curved shapes. Similarly,elements having polygonal (including rectangular, square andtriangular), round, and curved cross sections can be used. Thecombination of original cylindrical shape of the instrument andcylindrical-conic shape after heat treatment, which is most suitable forroot canal work, can be replaced by other shapes which might be moresuitable for specific applications. Additionally the structure of theinstrument need not be the same as the preferred embodiment of the SAFdescribed hereinabove. FIGS. 11A to 11F show cross-sections of someexamples of different embodiments of the instrument of the invention.The longitudinal elements are designated by numeral 20 and thecircumferential elements 21. FIG. 11A shows the SAF and FIG. 11B is asimilar design except that, in this embodiment, only the outer surfacesof the longitudinal elements are in contact with the canal wall. Usingthe embodiment of FIG. 11B, the debris can be removed upwards throughthe space between the canal wall and the circumferential elements whilefluid flows downwards through the center of the device, or vice versa.The embodiment of FIG. 11C is triangular shaped. The longitudinalelements can be round and covered with abrasive material or teeth orthey can be triangular shaped with the outward facing apex acting as acutting/scraping edge. The embodiment shown in FIG. 11D has a singlesquare longitudinal element with four blades attached to it. Theembodiments of FIG. 11E and FIG. 11F have a single longitudinal elementfrom which project radially a multitude of blade-like or wire-likeelements. The means of designing and manufacturing these and otherembodiments of the instrument of the invention, including providing thenecessary superelastic and shape memory properties is within the scopeof the knowledge of skilled persons and therefore will not be discussedin further detail herein.

In another embodiment, the instrument of the invention comprises a longnarrow balloon, which is inserted into the channel and then inflated.This embodiment can be realized in several ways. For, example, aninstrument based on the design of the SAF can be built in which thecircumferential elements are removed and a balloon is mounted to thedevice along its longitudinal axis and inside the longitudinal elements.The balloon is attached to the device at the neck and to the distal endsof the longitudinal elements. The instrument is inserted into the canalwith the balloon deflated. When in position, fluid is introduced intothe interior of the balloon using conventional techniques and theballoon expands pushing the longitudinal elements against the walls ofthe channel. The outer surfaces of the longitudinal elements are treatedor shaped in some way to enable them to remove material from the wall asthe instrument is moved relative to the walls of the channel. Withembodiments comprising a balloon, the relative motion is preferablytranslational, i.e. the instrument is alternately pushed and pulled inthe direction of the longitudinal axis of the channel.

In an alternate embodiment, the device can comprise a balloon only whichis coated with an abrasive material on its outer surface. To give theballoon sufficient rigidity, a rod or wire is inserted into the interiorof the balloon and attached at the distal end. The balloon is insertedinto the channel and then inflated pressing the sides of the balloonagainst the walls of the channel. The relative motion is preferablytranslational i.e. pushing and pulling the internal rod in the directionof the longitudinal axis of the channel will cause the balloon to moverelative to the wall cleaning, shaping, and widening the channel. Whenthe work is completed, the balloon is deflated and withdrawn from thechannel.

Although embodiments of the invention have been described by way ofillustration, it will be understood that the invention may be carriedout with many variations, modifications, and adaptations, withoutdeparting from its spirit or exceeding the scope of the claims.

BIBLIOGRAPHY

-   1. Saunders, W P, Saunders, E M, Sadiq, J, Cruickshank, E, Technical    standard of root canal treatment in an adult Scottish    sub-population, Br Dent J 182: 382-386, 1990.-   2. Wu, M-K, R'oris, A, Borkis, D, Wesselink, PR, Prevalence and    extent of long oval canals in the apical third, Oral Surg Oral Med    Oral Pathol 89:739-743, 2000.-   3. Tan, BT, Messer, H H, The quality of apical canal preparation    using hand and rotary instruments with specific criteria for    enlargement based on initial apical file size, J Endodon 28:    658-664, 2002.-   4. Wu, M-K, Wesselink P R, A primary observation on the preparation    and obturation of oval canals, In. Endod J 34:137-141, 2001.

1. An endodontic instrument for removing material from a wall of a rootcanal channel, the instrument comprising a hollow flexible member havinga longitudinal axis and an initial cross-sectional area in a planeperpendicular to the longitudinal axis at each point along thelongitudinal axis, the member comprising a wall having an openlattice-like structure surrounding a hollow interior portion of theinstrument, said open lattice structure comprising a plurality oflongitudinal elements extending generally parallel to the longitudinalaxis, and a plurality of connecting elements interconnecting betweensaid longitudinal elements, the member being bendable along the axis andresiliently compressible in cross-sectional area such that, wheninserted into a channel of cross-sectional area less than the initialcross-sectional area, the flexible member conforms to an internal shapeof the channel.
 2. The endodontic instrument of claim 1, wherein theflexible member is a shape memory member.
 3. The endodontic instrumentof claim 1, further comprising a cutting edge on at least a portion ofan exterior surface of the member.
 4. The endodontic instrument of claim1, further comprising on at least a portion of an exterior surface ofthe member at least one selected from a group consisting of an abrasivesurface, a roughened surface, small teeth, and a cutting edge.
 5. Theendodontic instrument of claim 4, wherein the instrument is made fromone selected from a group consisting of a superelastic material, amaterial having shape memory properties, and a material treated to givethe material shape memory properties.
 6. The endodontic instrument ofclaim 4, wherein the instrument is made from a nickel titanium alloy. 7.The endodontic instrument of claim 1, wherein, in an uncompressed stateof the flexible member, said longitudinal elements and said connectingelements lie substantially on a cylindrical profile.
 8. The endodonticinstrument of claim 7, wherein said longitudinal elements and saidconnecting elements define an open structure such that a majority of anarea of said cylindrical profile is open.
 9. The endodontic instrumentof claim 7, wherein at least part of each of said connecting elementsextends in a direction having a longitudinal component.
 10. Theendodontic instrument of claim 1, wherein the flexible member isresiliently compressible such that, when the flexible member is rotatedabout said longitudinal axis, the flexible member remains pressedagainst an internal surface of a non-circular channel.
 11. Theendodontic instrument of claim 1, wherein the channel is non-circular incross-sectional shape.
 12. An endodontic instrument for removin materialfrom a wall of a root canal channel, the instrument comprising: a hollowflexible member having a longitudinal axis and an initialcross-sectional area in a plane perpendicular to the longitudinal axisat each point along the longitudinal axis, the member comprising a wallhaving an open lattice-like structure surrounding a hollow interiorportion of the instrument, the member being bendable along the axis andresiliently compressible in cross-sectional area such that when insertedinto a channel of cross-sectional area less than the initialcross-sectional area the flexible member conforms to an internal shapeof the channel, wherein at least a portion of an exterior surface of themember comprises at least one selected from a group consisting of: anabrasive surface a roughened surface, small teeth, and a cutting edge,and wherein said open lattice-like structure comprises at least onelongitudinal element connected to a plurality of circumferentialelements.
 13. The endodontic instrument of claim 12, wherein thecircumferential elements are straight elements.
 14. The endodonticinstrument of claim 12, wherein the longitudinal element is one selectedfrom a group consisting of a straight element and a curved element, andwherein the circumferential elements are selected from a groupconsisting of straight elements and curved elements.
 15. An endodonticinstrument for removing material from a wall of a root canal channel,the instrument comprising a hollow flexible member having a longitudinalaxis and an initial cross-sectional area in a plane perpendicular to thelongitudinal axis at each point along the longitudinal axis, the membercomprising an open lattice-like structure comprising a plurality oflongitudinal elements extending generally parallel to the longitudinalaxis, and a plurality of connecting elements interconnecting betweensaid longitudinal elements, said longitudinal elements and saidconnecting elements together defining an external profile of the member,a majority of an area of said external profile being open, the memberbeing bendable along the axis and resiliently compressible incross-sectional area such that, when inserted into a channel ofcross-sectional area less than the initial cross-sectional area, theflexible member conforms to an internal shape of the channel.
 16. Theendodontic instrument of claim 15, wherein the flexible member is ashape memory member.
 17. The endodontic instrument of claim 15, furthercomprising on at least a portion of an exterior surface of the member atleast one selected from a group consisting of an abrasive surface, aroughened surface, small teeth, and a cutting edge.
 18. The endodonticinstrument of claim 15, wherein said longitudinal elements and saidconnecting elements together form an open lattice structure.
 19. Theendodontic instrument of claim 15, wherein the instrument is made fromone selected from a group consisting of a superelastic material, amaterial having shape memory properties, and a material treated to givethe material shape memory properties.
 20. The endodontic instrument ofclaim 15, wherein the instrument is made from a nickel titanium alloy.21. The endodontic instrument of claim 15, wherein, in an uncompressedstate of the flexible member, said longitudinal elements and saidconnecting elements lie substantially on a cylindrical profile.
 22. Theendodontic instrument of claim 15, wherein at least part of each of saidconnecting elements extends in a direction having a longitudinalcomponent.
 23. The endodontic instrument of claim 15, wherein theflexible member is resiliently compressible such that, when the flexiblemember is rotated about said longitudinal axis, the flexible memberremains pressed against an internal surface of a non-circular channel.